Turbulent Blood Flow in a Ventricular Assist Device

Application Challenge AC7-03 © copyright ERCOFTAC 2021

Description

Introduction

Ventricular Assist Devices (VADs) are implanted in patients with severe heart failure. Today, nearly all VADs are designed as turbomachinery, since they have a higher power density as pulsatile pumps, and therefore can be implanted within the human body.

By using Computational Fluid Dynamics (CFD), VADs must be designed and optimised in such a way that they reproduce a physiological pressure increase in order to sufficiently supply the body with enough blood flow. Furthermore, they must be designed in order to guarantee that the blood, which passes the VAD, is not damaged due to non-physiological flow conditions (high shear stresses, stagnation areas, high turbulent kinetic energy (TKE) regions, ...) in the device.

The CFD simulation in a VAD can be challenging, since the inflow is laminar and all turbulence is produced within the pump and decays shortly after the pump outlet. Furthermore, pump Reynolds number $Re_{p}={u_{2}D_{2}}/{\nu }$ is small with $Re_{p}=10^{3}-10^{4}$ compared to industrial pumps ( $Re_{p}\approx 10^{6}$ ), and transition might occur.

In this respect, the aim of this study is to investigate the suitability of different URANS methods (with different turbulence models and solver settings) for the flow computation in an axial VAD. Furthermore, the influence of the grid resolution will also be investigated based on a extended grid study. The flow fields of the URANS simulations will be compared with a highly turbulence-resolving large-eddy simulation. Here, both fluid mechanical parameters, such as the pump characteristics and velocity fields, as well as haemodynamic parameters, such as the haemolysis index MIH or stagnation zones, are investigated.